Device for setting the length of a top link of an attaching device of a tractor

ABSTRACT

A device for setting the length of a top link ( 7 ) of an attaching device of a tractor ( 1 ) has a piston/cylinder unit ( 14 ) for length setting purposes. The piston/cylinder ( 14 ) has a displacement sensor ( 20 ) which records the respective actual length setting of the top link ( 7 ). The displacement sensor ( 20 ) generates an actual proportional length signal. A lift position sensor ( 13 ) is provided which generates an electric signal representing the respective actual lift position of the lower steering arms ( 4 ). A nominal length setting of the top link ( 7 ), which refers to the respective actual lift position, can be stored in a storage unit ( 33 ). When a new actual lift position is reached during the automatic mode of operation, it is possible to generate an electric control signal which corresponds to the nominal length setting of the top link ( 7 ). The signal is transmitted to the comparator of a control unit ( 34 ). The comparator compares the control signal with the actual length signal. The control unit controls the piston/cylinder ( 14 ) as a function of the deviation of the signals from one another, towards a nominal length setting. In this way it is possible, automatically, to achieve optimum kinematics for an implement attached to a tractor, without any outside interference.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority upon German application 197 47 949.9filed Oct. 30, 1997, which is incorporated herein by reference.

BACKGROUND OF THE INVENTION

The invention relates to a device for setting the length of a top linkof a tractor attaching device. The attaching device, apart from a toplink, also includes two lower steering arms. The two lower steering armsare arranged so as to be laterally displaced from the longitudinal axisof the tractor and are articulatably attached at one end. The top linkhas a power drive which is used for length setting.

A publication entitled “Hydraulic Top Link with Hook” of GKNWalterscheid GmbH, Lohmar, Germany (TAS 156/ID/GB/F 996 G10-I309562)describes a top link with a hydraulic cylinder used as a power drive. Ithas a double-acting piston-cylinder unit with a twin return valve(double check valve). The valve serves to block the set length even inthe case of longer periods of rest. A marking rod is also provided,which facilitates handling.

Achieving the optimum length setting for the top link when the tractoroperates with an attached implement requires considerable experience.The operative always has to carry out a manual operation to adapt thelength setting. This is labor-intensive and optimum kinematic conditionsfor the respective implement are not achieved.

SUMMARY OF THE INVENTION

It is an object of the present invention to provide a device whichachieves optimum kinematics in operation for each attached implement.

In accordance with the invention, a device for setting the length of atop link forms part of an attaching device of a tractor. A displacementsensor is provided which records the respective actual length setting ofthe top link. The sensor generates an electric actual length signalwhich represents the actual length setting. A lift position sensor ispresent to generate an electric signal which represents the actual liftposition of the lower steering arms. A storage unit is present to storea nominal length setting of the top link. The nominal length settingrelates to the respective actual lift position. When a new actual liftposition is reached, the storage unit generates an electric controlsignal corresponding to the nominal length signal. The control unitactuates the power drive as a function of the deviation of therespective actual length setting from the control signal.

An advantage of this embodiment is that the respective kinematics meetgreatly differing requirements. The operative is offered specificfunctional improvements and greater comfort. It is possible to achievekinematics which are adapted to a specific implement. The requiredpredetermined values may be entered by hand. It is also possible toenter into the storage unit a specific tractor/implement combination inthe form of a special program.

According to a further embodiment, the respective nominal lengthsettings relative to the associated lift positions can be stored in thestorage unit in the form of a curve. In this context, the two end pointsof the curve are stored in the storage unit by moving to the highestlift position, in combination with a first nominal length setting and,respectively, to the lowest lift position, in combination with a secondnominal length setting of the top link with the implement connected tothe attaching device. This means that the end points of the curve can beadapted for each tractor/implement combination. For most applications,the curve may be presented by a straight line extending between the endpoints. However, it may also be necessary to store a special curve. Thedecisive factors are the two end points which are stored by a so-called“teach-in” method. Accordingly, while the end positions are stored, itis also possible to store intermediate positions between the two endpositions. The intermediate positions may be individually stored. Theintermediate positions are created by lifting the lower steering arms toa first position, then manually adjusting the top link to a position sothat the implement attached to the lower steering arms and the top linkassumes the first position. Thus, this given lifting position of thelower steering arms is stored as an intermediate position. This processmay be carried out to produce additional intermediate positions.

The invention can be complemented by arbitrarily changing the curve bychanging the length setting of the top link. Thus, a curve is obtainedwith a discontinuity from which two straight lines are assumed to extendto the end points. Finally, it is possible to store curves for severaldifferent implements in the storage unit. Thus, the curves may beactivated when the respective implement is connected to the attachingdevice.

In a preferred embodiment, the power drive for the top link is ahydraulically loadable piston/cylinder unit. The control unit ispreferably a microprocessor. It is possible to select differentoperational conditions. Thus, the respective nominal length setting forthe top link represents a function of the lift position of the lowersteering arms.

The control means permit different operational conditions which can bedetermined, for instance, by an operation selection switch. In a firstposition, for instance in the “off” position, the control unit isdeactivated and the length of the top link cannot be changed. In asecond selectable position, the “automatic” position, it is possible toautomatically control the length of the top link as a function of theposition within control range limits. Outside the control range limits,the length remains constant.

A third type of operation exists, the “floating position”. This positiondiffers from the automatic type of operation in that the length betweenthe control range limits is not controlled. The power drive of the toplink is disconnected. Furthermore, a “manual” type of operation ispossible. Here, the length of the top link is set by hand. In this case,the power drive is controllable by hand, so that any kind of setting ispossible.

Further, in the “automatic” position and in the “floating” position, itis possible to superimpose manual operation. This permits temporaryadjustments, for instance, changing the angle of attack of the workingtool. Finally, it is possible, in addition to manual control facilities,to provide remote control means. This permits control by radio or by acable connection. These control means permit the most variedrequirements to be met by the kinematics. The user benefits fromspecific functional improvements and greater comfort.

From the following detailed description, taken in conjunction with theaccompanying drawings and subjoined claims, other objects and advantagesof the present invention will become apparent to those skilled in theart.

BRIEF DESCRIPTION OF THE DRAWINGS

The drawing diagrammatically shows a tractor and an attached implementas well as the attaching device. Also, part of the device forcontrolling the length settings is shown. Further, the drawings show anumber of variants regarding the curves which are used. The design andmode of operation of the device in accordance with the invention areexplained in greater detail with reference to the following drawingswherein:

FIG. 1 is a diagrammatic view of a tractor with an implement connectedto the attaching device of the tractor.

FIG. 2 is a diagrammatic view of a design of the device in accordancewith the invention in combination with other components of the attachingdevice.

FIG. 3 is a schematic view of a first type of curve which may be usedfor operating an implement in connection with the tractor carrying theimplement.

FIG. 4 is a schematic view of a curve in the operational “floating”position.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

FIG. 1 illustrates a tractor 1 with an attached implement. The tractor 1is drivable on the ground 3 which is intended to be worked by theimplement 2. At the rear of the tractor 1, two lower steering arms 4 areprovided which are laterally displaced from the longitudinal axis. Oneend of the arms is articulatably connected to the tractor 1. The otherend of the arms is provided with a coupling hook 5. Only one of the twolower steering arms 4 is shown. The coupling hooks 5 of the lowersteering arms 4 are connected to corresponding coupling means 6 of theimplement 2. Above the two lower steering arms 4, a top link 7 isconnected by an articulated connection 8 to the rear of the tractor. Atits free end, the top link 7 is provided with a coupling hook 9. Thecoupling hook 9 is connected to coupling means 10 at the implement 2.

The two lower steering arms 4 are each connected by a lifting strut 12to a lifting arm 11. The lifting arms are connected to a power drive forthe purpose of setting the height of the coupling point represented bythe coupling hook 5 receiving the implement 2. The lifting arm 11 isassociated with a lift position sensor 13. The sensor 13 generates asignal which is proportional to the lift position of the lower steeringarm 4.

FIG. 2 shows the design of an attaching device having a lower steeringarm 4, the connected coupling hook 5, the lifting strut 12 for settingpurposes, the lifting arm 11 connected to the strut 12, and the liftposition sensor 13. Furthermore, the top link 7 is shown in detail. Thetop link 7 is a hydraulic top link with a piston/cylinder unit 14. Theunit has a cylinder housing 15. One end of the housing is engaged bymeans providing an articulated connection with the tractor.

A piston 16 is displaceably received in the cylinder housing 15. At itsend projecting from the cylinder housing 15, the piston rod 17 connectedto the piston 16 carries the coupling hook 9. The top link is shown inits retracted position where the actual length setting is represented bythe reference number 21. This means that the piston 16 is in itsfurthest retracted position. Thus, the cylinder chamber 19 at the pistonend is at its minimum. The cylinder chamber 18 at the piston rod end isat its maximum.

The cylinder housing 15 is associated with a displacement sensor 20. Thesensor 20 is connected to the base of the cylinder housing 15. The baseis remote from the coupling hook 9. The sensor 20 includes a bar-shapedportion which projects into a bore of the piston 16 and the piston rod17, respectively. The sensor 20 transmits an electric actual lengthsignal representing the respective actual length setting 21 to a controlline 27. The control signal is transmitted by the control line 27 to acontrol unit 34.

The lift position sensor 13 is connected by a control line 35 to thestorage unit 33. The lift position sensor 13 generates an electriccontrol signal which is proportional to the lift position of the lowersteering arms. The storage unit, in turn, is connected by a control line28 to the control unit 34.

The curves stored in the storage unit 33 can be activated for a specificimplement and fed in by the “teach-in” method. Thus, via the controlline 28, the control unit 34 is provided with a nominal length settingof the top link 7 associated with each specific lift position. Thenominal length setting signal, when a corresponding lift position isreached, is transmitted by the lift position sensor 13, via the controlline 35, to the storage unit 33. The signal is passed onto the controlunit 34 in the form of an electric control signal. The control unit 34has a comparator which generates a control signal. The control signalactuates a switching valve 24 as a function of the deviation of theactual length setting of the top link 7 from the nominal length setting.

The switching valve permits different positions which will be describedin greater detail below. The switching valve includes two ports leadingto the top link 7. The ports establish a connection with the firstconnecting line 22, the second connecting line 23, a pressure line 25connected to a pump or pressure agent supply source of the tractor, areturn line 26 leading to the tank, or the ports establish a connectionrelative to one another.

In the position as indicated, the switching valve 24 is in the shut-offposition. This means that the two connecting lines 22, 23 aredisconnected from the pressure line 25 and from the return line 26. Ifthe switching valve 24 is switched in the direction of arrow A by oneposition, the two connecting lines 22, 23 are connected to one anotherand to the return line 26. The connection with the pressure line 25remains shut off. In this position, the actual length setting 21 can bechanged freely. This position is the “floating position” which can bepredetermined by a pre-selection switch 32. An exchange of pressureagent takes place between the cylinder chamber 18 at the piston rod endand the cylinder chamber 19 at the piston end via the connecting line22, 23. The lines 22, 23 are short-circuited relative to one another.As, when shortening the length setting, more volume flows out of thecylinder chamber 19 at the piston end than can be accommodated by thecylinder chamber 18 at the piston rod end. The additional volume escapesthrough the port leading to the return pipe 26. This operating positionis chosen, if the attached implement engages the ground and if the toplink 7 only has a guiding function without having to accommodate anyforces in sense of carrying the implement. Such a mode of operation isalso obvious from the curve shown in FIG. 4.

If the control unit 34 indicates that the nominal length setting,starting from an actual length setting, requires an increase in thelength of the top link 7, when the operation selection switch 32 is setto “automatic”, the switching valve 24 is switched in direction A. Inthis position, the pressure line 25 is connected to a first connectingline 22 leading to the cylinder chamber 19 at the piston end. The secondconnecting line 23, connected to the cylinder chamber 18 at the pistonrod end, is connected to the return line 26. In this position, theactual length setting 21 is increased. Thus, the piston rod 17, with thecoupling hook 9, moves out of the cylinder housing 15. The cylinderchamber 19 at the piston end is filled with pressurized fluid. Thecylinder chamber 18 at the piston rod end is emptied, via the secondconnecting line 23 and the return pipe 27 towards the tank. This processcontinues until the nominal length setting, transmitted via the storageunit 33 to the control unit 34, corresponds to the actual lengthsetting.

If the storage unit, as a result of the position of the lower steeringarm 4, specifies, via the position sensor 13, a position which requiresshortening of the top link 7, starting from its actual length settingwhich is provided by the control unit 34 comparator by comparing thesignal of the displacement sensor 20 with that predetermined by thestorage unit 33, the switching valve 24 is switched in the direction ofarrow B. Thus, a connection is made between the pressure line 25 and thesecond connecting line 23. Furthermore, a connection is made between thefirst connecting line 22 and the return line 26. In this way, thecylinder chamber 18 at the piston rod end is pressured with pressurizedfluid. The pressurization continues until the comparison of the controlsignal of the displacement sensor 13, with the signal transmitted to thecontrol unit 34, towards the nominal length setting, has resulted incorresponding values. In addition to the two positions as describedabove, the operation selection switch 32 also has an “off” position. The“off” position corresponds to the illustrated shut-off position in whichan exchange of pressure agent cannot take place and the actual lengthsetting 21 remains the same.

In addition, the operation selection switch 32 has a position in whichthe switching valve 24 can be switched manually in order to achieve therequired nominal length setting of the top link 7. Further, the controlsignals of the control unit 34 can also be superimposed manually. Thus,the switching valve 24 can be switched arbitrarily. This switching leadsto a temporary change in the length setting of the top link 7.

FIG. 3 describes a possible mode of operation and shows a diagramcontaining the length of the top link expressed in percent of themaximum top link length as a function of the height of the lift positionof the lower steering arms.

The device in accordance with the invention enables a directspecification of a curve 42 or the assumption of a straight line betweenthe two end points 36, 37. The two end points can be determined by the“teach-in” method when an implement is attached to a tractor, thus doingjustice to the special tractor/implement combination. The end point 36characterizes the lower limit position. Thus, end point 36 is the lowestend point which is represented by the control range limit 40 and thesecond nominal length setting. Outside the control range limit 40, afurther increase in length is not possible. Thus, the lower limit value38 remains constant. This also applies to the upper limit value which,together with the control range limit 41, defines the upper limitposition 37 and thus the upper end point 39.

In the present case, the curve 42 between the two end points 36, 37 isassumed to be a straight line. Thus, a linear change (percent) in thetop link length exists as a function of the change in the height of thelift position from a minimum towards a maximum between the two controlrange limits 40, 41. If, as a result of special conditions, a manualoperation is needed, the top link length can be temporarily changed.Thus, a new nominal value 43 is set as a result of the control meansbeing manually superimposed.

Thus, a new curve 44 is obtained with a discontinuity in the range ofthe new nominal value 43. If subsequently the length is automaticallyfurther increased, the top link length is adapted in accordance with thetwo straight lines between the end points 36 and 37 and thediscontinuity 43 existing therebetween. The arms of the new curve haveeach been given the reference number 44.

FIG. 4 also shows a diagram where the top link length (OL-length) isexpressed as a percent of a total length. The height of the liftposition from a minimum to a maximum is entered vertically andhorizontally. Again, there exists outside control range limits in whicha change in the top link length cannot take place. This is representedby the two upper and lower limits 38′, 39′. Between the two end points36′, 37′, any setting is possible. Here, the operation selection switchis switched to a “floating position”. In consequence, the curve 42′ canhave any form between the end points 36′, 37′. If, as a result ofspecial conditions, manual operation is necessary, such as theelimination of the floating position, the top link length can betemporarily changed. Thus, as a result of the control means beingsuperimposed, a nominal value 43′ is obtained. The control system nowoperates within the control range limits 40, 41. This is analogous tothe automatic mode of operation and a new curve 44 is obtained. When thecontrol range limits 40, 41 are exceeded, a constant length is setoutside the control range. However, while inside the control range, thefloating position is permitted again.

While the above detailed description describes the preferred embodimentof the present invention, the invention is susceptible to modification,variation and alteration without deviating from the scope and fairmeaning of the subjoined claims.

What is claimed is:
 1. A device for setting the length of a top link ofan attaching device of a tractor, the attaching device, apart from thetop link, comprising: a top link; two lower steering arms; a power drivecoupled with said top link for providing length settings of said toplink; a displacement sensor for generating an electric actual lengthsignal which represents the respective actual length setting of the toplink; a lift position sensor for generating an electric signalrepresenting the actual lift position of the lower steering arms; astorage unit for storing a nominal length setting of the top link, saidnominal length setting relates to the respective actual lift position,and the respective nominal length settings can be stored in the storageunit relative to the associated lift positions in the form of a curve,and when a new actual lift position is reached, said storage unitgenerates an electric control signal corresponding to the nominal lengthsetting of the top link; and a control unit including a comparatorcomparing the control signal with the actual length signal and actuatingthe power drive as a function of the deviation of the respective actuallength signal from the control signal.
 2. A device according to claim 1,wherein two end points of the curve can be stored in the storage unit bymoving to the highest lift position in combination with a first nominallength setting and, respectively, to a lowest lift position incombination with a second nominal length setting of the top link withthe implement connected to the attaching device.
 3. A device accordingto claim 2, wherein the curve is represented by a straight lineextending between the end points.
 4. A device according to claim 3,wherein the curve can be changed by arbitrarily changing the lengthsetting of the top link into a curve with a discontinuity and twostraight lines extending from said discontinuity to the end points.
 5. Adevice according to claim 2, wherein curves for several differentimplements can be stored in the storage unit and activated therefrom.